The use of polypropylene as a textile fiber has a greatly increased in recent years. Various physical characteristics of polypropylene in fiber form and in knit or woven fabrics can be quite attractive and recent developments in formulations for producing polypropylene fibers have produced fabrics with greatly improved hand, and drape, color retention, etc. However, to the present applicant's knowledge, no successful methods for producing a fire retarding polypropylene has been found which can pass the NFPA (National Fire Protection Association) 701 vertical test and which does not so greatly alter the physical characteristics of such fabrics so that the basic attractiveness and utility of the polypropylene fiber has been rendered essentially worthless. One of the basic reasons for this result is that the addition of flame retardant chemicals according to current methods to produce the desired effect is in the range of 50%-80% by weight of polypropylene. Not only can this method be prohibitively expensive but also the important physical characteristics of the fabric greatly deteriorate.
One of the problems associated with the flame retardancy of polypropylene is caused by its high heat of combustion (11,600 cal/g) where for example cotton, polyester and rayon have heats of combustion which are respectively 4,330, 6,170 and 3,446 cal/g. Another problem is its relatively low Limiting Oxygen Index (LOI), i.e. 18.6, which is defined as the minimum percentage of oxygen in the environment (e.g. air) necessary to sustain combustion.
Additives used for the flame retardation of polypropylene include the use of halogens, chlorine or bromine with and without antimony oxide as a synergist and phosphorus compounds. Flame retardant agents are sometimes added to the melt before spinning to give some fire retardancy and bromine compounds are favored over chlorine compounds as being more effective for polypropylene fire retardancy. Heretofore, the use of these compounds has not permitted polypropylene to pass NFPA 701. The use of decabromodiphenyl oxide "Deca" with antimony oxide as a synergist in combination with a halogenated binder such as PVC has been recommended. However, so much chemical has been required to produce some flame retardant characteristics in polypropylene that the fabric weight is increased by 50-80%. Furthermore, deca is expensive ($1.15 per sq. yd.) and is a solid chalky powder which gives a scratchy feel to the fabric causes the fabric to turn white.
The method of the present invention has succeeded in producing acceptable fire retardancy for polypropylene fibers as a spin finish, as well as woven polypropylene fabrics used as wall and panel fabrics and upholstery. Fabrics treated in accordance with the method of the invention successfully pass the stringent National Fire Protection Association vertical test NFPA 701 without first having to remove coning oils, i.e., surface oils which were added to aid yarn handling and wearing. The treated fibers and the fabrics so treated have superior hand and drape and are resistant to seam-slip. Flame retardancy continues throughout 25 washings. The chemical treatment is inexpensive and is less that 1/10 of the cost of less effective treatments recommended in the literature.